Real-time Model-based Image Color Correction for Underwater Robots

Recently, a new underwater imaging formation model presented that the coefficients related to the direct and backscatter transmission signals are dependent on the type of water, camera specifications, water depth, and imaging range. This paper proposes an underwater color correction method that integrates this new model on an underwater robot, using information from a pressure depth sensor for water depth and a visual odometry system for estimating scene distance. Experiments were performed with and without a color chart over coral reefs and a shipwreck in the Caribbean. We demonstrate the performance of our proposed method by comparing it with other statistic-, physic-, and learning-based color correction methods. Applications for our proposed method include improved 3D reconstruction and more robust underwater robot navigation.Comment: Accepted at the 2019 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS

A Robust Quasi-dense Matching Approach for Underwater Images

While different techniques for finding dense correspondences in images taken in air have achieved significant success, application of these techniques to underwater imagery still presents a serious challenge, especially in the case of “monocular stereo” when images constituting a stereo pair are acquired asynchronously. This is generally because of the poor image quality which is inherent to imaging in aquatic environments (blurriness, range-dependent brightness and color variations, time-varying water column disturbances, etc.). The goal of this research is to develop a technique resulting in maximal number of successful matches (conjugate points) in two overlapping images. We propose a quasi-dense matching approach which works reliably for underwater imagery. The proposed approach starts with a sparse set of highly robust matches (seeds) and expands pair-wise matches into their neighborhoods. The Adaptive Least Square Matching (ALSM) is used during the search process to establish new matches to increase the robustness of the solution and avoid mismatches. Experiments on a typical underwater image dataset demonstrate promising results

Phenomenological marine snow model for optical underwater image simulation: Applications to color restoration

International audienceOptical imaging plays an important role in oceanic science and engineering. However, the design of optical systems and image processing techniques for subsea environment are challenging tasks due to water turbidity. Marine snow is notably a major source of image degradation as it creates white bright spots that may strongly impact the performance of image processing methods. In this context, it is necessary to have a tool to foresee the behavior of these methods in marine conditions. This paper presents a phenomenological model of marine snow for image simulation. In order to highlight the interest of such a modeling for image processing characterization, the impact of marine snow perturbation on a color restoration technique is analyzed and a solution to improve the robustness of the algorithm is finally proposed

Field deployable dynamic lighting system for turbid water imaging

Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2011The ocean depths provide an ever changing and complex imaging environment. As scientists and researches strive to document and study more remote and optically challenging areas, specifically scatter-limited environments. There is a requirement for new illumination systems that improve both image quality and increase imaging distance. One of the most constraining optical properties to underwater image quality are scattering caused by ocean chemistry and entrained organic material. By reducing the size of the scatter interaction volume, one can immediately improve both the focus (forward scatter limited) and contrast (backscatter limited) of underwater images. This thesis describes a relatively simple, cost-effective and field-deployable low-power dynamic lighting system that minimizes the scatter interaction volume with both subjective and quantifiable improvements in imaging performance

MODELLING COLOUR ABSORPTION OF UNDERWATER IMAGES USING SFM-MVS GENERATED DEPTH MAPS

Abstract. The problem of colour correction of underwater images concerns not only surveyors, who primarily use images for photogrammetric purposes, but also archaeologists, marine biologists, and many other domains experts whose aim is to study objects and lifeforms underwater. Different methods exist in the literature; some of them provide outstanding results but works involving physical models that take into account additional information and variables (light conditions, depths, camera to objects distances, water properties) that are not always available or can be measured using expensive equipment or calculated using more complicated models. Some other methods have the advantages of working with basically all kinds of dataset, but without considering any geometric information, therefore applying corrections that work only in very generic conditions that most of the time differs from the real-world applications.This paper presents an easy and fast method for restoring the colour information on images captured underwater. The compelling idea is to model light backscattering and absorption variation according to the distance of the surveyed object. This information is always obtainable in photogrammetric datasets, as the model utilises the scene's 3D geometry by creating and using SfM-MVS generated depth maps, which are crucial for implementing the proposed methodology. The results presented visually and quantitatively are promising since they are an excellent compromise to provide a straightforward and easily adaptable workflow to restore the colour information in underwater images

Solar radiative transfer into the ocean: A study on underwater light fluctuations due to surface waves

The thesis is about the solar radiative transfer into the ocean. Particular emphasis is placed on underwater light fluctuations due to focusing surface waves. The study includes measurements at high sea and computational simulations of the light propa-gation in seawater and wave-induced radiative variability. Surface waves of different sizes have an optical lensing effect; they cause focusing of light beams at various depths. The underwater propagation of light depends on the scattering and absorption properties of seawater. Strongest light fluctuations appear near the surface at water depths of 0.5 to 10 m. At 1 m depth, radiative enhancements with a factor of 40 compared to the mean light level can be achieved. These short-term extreme values refer to the downwelling irradiance. The reason for the most intense irradiance peaks are surface waves with lengths of 20 cm to 5 m. In theory, light flashes with a radiative intensification of the factor 1.5 can appear down to 80 m of water depth. The range of possible irradiance peaks is discussed with respect to all relevant ocean waves. Even 200 m long swell waves can originate small irradiance changes below the 90 m depth level. In natural sea states waves of different sizes are superposed. Their respective lensing effect controls the subsurface light regime. The mechanisms of those interactions are analyzed. Local wind, which is primarily associated with ultra-gravity waves, strongly affects light fluctuations within the near-surface region down to 10 m depth. The most intense radiative peaks result from moderate wind conditions with velocities of 2 to 7 m s-1. Below 10 m depth, the temporal and spatial light variability is driven by super-posed fully developed gravity waves of the corresponding sea state. Comparable strong variations arise from 1.5 m high waves. Even in 100 m depth slight wave-induced light field variance was found